The most common and most likely answer to this crossword clue is the 9 letter word WHIRLIGIG
I've seen this crossword clue in The Guardian
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More clues leading to the result WHIRLIGIG
Buddy explains!

The straight part
We know that "merry-go-round" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case merry-go-round = whirligig.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WHIRLIGIG mean?
WHIRLIGIG noun- Anything that whirls or spins around, such as a toy top or a merry-go-round.
- A device incorporating spinning, wind-driven propellers or pinwheels, used as whimsical outdoor decoration in a garden or on a porch.
- A whirligig beetle.
- A device for punishing prisoners, comprising a wooden cage that rapidly spins around.